The present invention relates generally to integrated circuit memory devices and, more particularly, to a piezo-driven, low temperature, low power, non-volatile memory cell having hysteretic resistance.
There are numerous contemporary applications where a compact, non-volatile memory with no moving parts would be an enabling technology. Such examples include portable computing and communication devices, computers that use low power, etc. Current techniques for achieving non-volatile memory include magnetic random access memory (MRAM), FLASH, and ferroelectric random access memory (FeRAM). At the present time, the capacities and speeds of these memories in practical devices are comparable with the capacities of dynamic random access memory (DRAM) chips, which is a volatile type of memory that requires continuous power in order to retain the data therein. In addition, DRAM is also relatively slow. Regardless, none of these types of memory described above can compete with the high volumes in disk storage.
A new technology, Phase Change Material (PCM), is now becoming available and is well-suited for non-volatile memory technology. One exemplary phase change material in this regard is a ternary alloy of germanium (Ge), antimony (Sb) and tellurium (Te) (GST), with a typical composition being Ge2Sb2Te5, also referred to as GST 225. The GST material is interconvertible between two discrete states, amorphous (high electrical resistance) and crystalline (low electrical resistance), thereby enabling data storage therein. The interconversion or write process for these exemplary materials is done by thermal cycling of the PCM.
However, those types of PCMs (such as GST) that are programmed by internal heating also require a relatively large drive transistor capable of sourcing adequate current/power for the RESET portion of the PCM thermal programming operation. Moreover, such devices are difficult to locate in the back end of line (BEOL) region of a semiconductor device, due to the risk of damage to thermally sensitive low-K materials. In addition, as a result of elemental migration/diffusion at high programming temperatures, the amount of programming cycles that such devices may be subjected to (i.e., its endurance) is somewhat questionable for conventional memory use.
Accordingly, it would be desirable to be able to incorporate PCMs (and more generally, materials having a hysteretic programmable resistance) for non-volatile memory devices in a manner that avoids any disadvantages associated with thermal programming of the materials.